$ B = \left[\begin{array}{rrr}2 & 2 & 2 \\ 1 & 2 & 2 \\ 0 & 0 & 1\end{array}\right]$ What is $ B^{-1}$ ?
$ = \left[\begin{array}{rrr}1 & -1 & 0 \\ -\frac{1}{2} & 1 & -1 \\ 0 & 0 & 1\end{array}\right]$